The invention pertains to a locking mechanism for a device to modify the control timing of cylinder valves of an internal combustion engine, and especially to a vane-cell positioning device, including a drive wheel designed as an external rotor driven by a crankshaft of the internal combustion engine through a traction means, said drive wheel having a cavity formed by a perimeter wall and two side walls. The locking mechanism also includes an impeller that is placed in this cavity and designed as an internal rotor, permanently connected to a camshaft of the internal combustion engine. This impeller has at least one vane on the perimeter of its hub located in an axial notch and extending radially out from the hub. In the cavity of the drive wheel, at least one working chamber is formed by intermediate walls starting at the inside of the perimeter wall of the drive wheel and extending toward the longitudinal centerline of the device. Each of these working chambers is itself divided into two hydraulic pressure spaces by a vane of the impeller that extends into each working chamber. These hydraulic pressure spaces effect a pivoting motion and/or a fixing of the impeller with respect to the drive wheel by selectively, simultaneously, or with a time delay applying pressure from a hydraulic pressure medium. When the pressure is not applied in either of the pressure spaces, the impeller and the drive wheel can be coupled with one another mechanically in at least one preferred position with respect to one another.
A device of this type has already been categorized by patent U.S. Pat. No. 48,58,572. In a preferred embodiment of this device, six equally sized working chambers are formed between six intermediate walls located in the cavity of the drive wheel opposite one another in a circular direction. These working chambers themselves are each divided into a first and a second pressure space, which are liquid-tight with respect to one another, by means of six vanes fastened rigidly to the hub of an impeller connected to the camshaft. The mechanical coupling between the impeller and the drive wheel of the device is accomplished through either one of two spring-loaded locking pins located in a radial hole in an intermediate wall of the drive wheel engaging into a radial receiving hole located between two vanes of the hub in alternating fashion. This occurs when the vanes of the impeller are at one of their two end positions at the intermediate walls of the drive wheel and if the applied pressure from the hydraulic pressure medium is turned off at the first or second pressure space of the device. If, then, the pressure is reapplied to the respective pressure space and a specific value of the pressure of the pressure medium is exceeded, the respective locked locking pin is pushed completely into the radial hole in the intermediate wall and out of the receiving hole in the hub so that the mechanical coupling between the impeller and the drive wheel is again disengaged.
Another possibility of mechanical coupling between the impeller and the drive 20 wheel is suggested by the solution published in patent DE-OS 196 23 818. This solution is specifically intended for a pivoting-vane positioning device, which is comparable with respect to its basic design to a vane-cell positioning device, but with more massive vanes at the impeller and differing from it at most by only one to four working chamber(s). In this solution, an axial locking pin is located within one of the radial vanes of the impeller. This locking pin can be shifted parallel to the longitudinal centerline of the device and when the pressure of the hydraulic pressure medium decreases it is pushed by the force of a spring into an axial engagement opening in a front plate that is connected to the drive wheel. The engagement opening is hydraulically connected to one of the pressure spaces inside the device so that the pressure medium can also act on the front surface of the locked locking pin located in the engagement opening. When a certain value of pressure of the pressure medium is exceeded, the pressure medium pushes this pin again into its unlocked position within the vane.
However, these mechanical couplings between the impeller and the drive wheel of a vane-cell or pivoting-vane positioning device, in one case designed as a radial locking pin and in the other case designed as an axial locking pin, have the disadvantage in that they are constructed from a number of additional individual parts. Due to the necessary increase in expense to manufacture and install these parts, this raises the manufacturing costs of a vane-cell or pivoting-vane positioning device designed in this manner. Moreover, the danger exists in the design of the locking pin as simple pressure pins in both variations in that they deform when large stresses are absorbed from either rotating direction of the impeller, such that re-locking the device correctly can no longer always be guaranteed in every case. Also, the front surface of these types of locking pins, designed as pressure pins, is designed to be relatively small as a pressure application surface used for unlocking so that the pressure of the pressure medium sufficient to unlock only builds relatively late in the process, thus delaying the unlocking time of the device, which is detrimental.